The invention relates to a technique by which unauthorized publication and copying of electronic information can be exposed. The electronic information means particularly documents and programs distributed in an Internet type network.
The copying of electronically distributed information is technically very simple. For example, illegal copying of computer programs causes annual losses of milliards of dollars to software industry. Pirate copies are also a major problem in video and recording industry.
The common feature of all such information is that any protection of the information is based on copyright (or closely related forms of protection, such as data base protection), an agreement, or non-disclosure obligation. As previously known, the essential difference between copyright and industrial protectionxe2x80x94such as patent and design protectionxe2x80x94is that in industrial protection infringement is sufficiently shown if products can be shown to be similar, whereas to show infringement of copyright it must be shown that a product has been copied rather than created independently. The same applies not only to copyright, but also to infringement of commercial secrets and other non-disclosure obligations. Such infringement is particularly difficult to prove in respect of databases where information is, in principle, available to anyone, and any additional value produced by the information provider is based on advantageous selection or presentation of information. In the present application, the term xe2x80x98copyrightxe2x80x99 should thus be understood in the wide sense to comprise commercial secrets, non-disclosure obligations, etc. as well as the actual author""s rights. Correspondingly, a xe2x80x98copyright proprietorxe2x80x99 here refers to anyone who wants to prevent and/or expose unauthorized copying and/or publication of information.
Even if the copyright proprietor is able to show that the product has been copied without permission, he must also be able to indicate who is responsible for the copying. If an unauthorized copy is found in the possession of an end user who has bought the product in good faith, no compensation can usually be required from the end user. Further, the end user cannot be required to be able to or willing to expose who has sold the product.
For example, software suppliers use technology in which the software asks the user for his name and contact information in connection with the first installation. The information can be encoded in protected form and stored on an installation diskette. On the basis of this information the installation program produces a client identifier, which the client needs as he phones the supplier""s telephone support. By monitoring incoming calls and their client identifiers the supplier may be able to expose unauthorized copying. The technology, however, has many defects and restrictions. For example, the technology is based on the assumption that the user will at some point need telephone support. This, however, is not always a correct assumption. Most information can be used even without obtaining subsequent support from the supplier. Since upon installing the software, the dishonest user can supply any contact information whatsoever, it is not always possible to conclude from the unauthorized copy where the copy has been made. By comparing installations conducted with different user information, the unauthorized user can conclude where on the disk the user-specific information is located, and change the information. The technique cannot be applied to protecting text and image files, since the added information is easy to delete.
It is also known to slightly modify e.g. the character spacing, font size, etc. in text documents. The idea is that the user will not notice if there are, for example, a few 11-point characters amidst 12-point text. This solution is previously known e.g. from U.S. Pat. No. 5,467,447. The technology, however, cannot be used for protecting electronically distributed text, since the unauthorized user can simply impose the same layout on all text. Even if a so protected text is delivered on paper, the dishonest user can supply the text to a text scanner, which removes all extra formatting.
The object of the invention is thus to develop a technique by which unauthorized copying of electronically distributed information and the person responsible for the copying can be exposed. The objects of the invention are achieved with a technique that is characterized by what is stated in the independent claims. The preferred embodiments of the invention are claimed in the dependent claims.
The invention is based on the idea that the electronically distributed information is marked, i.e. modified to be different for each user. The modifications are not based on formatting, which can be easily changed, but are buried deep in the bit stream that carries the information. Differences are introduced in so many places in the versions delivered to different users that the unauthorized user cannot detect all the differences, or that it is not economically sensible to attempt to detect all the differences.
A known technique in which the information to be produced is marked in order to expose unauthorized publication comprises the steps of
defining a user identifier,
creating a source file containing a substantial part of the information produced, and
creating a different target file for each user on the basis of the source file and the user identifier.
The method of the invention further comprises the steps of
storing, in a file, several predefined modification rules for modifying the information contained in the source file, and
by means of a digital processor:
generating a sequence of modification keys on the basis of the user identifier,
defining the locations in the source file that are to be modified and making modifications in these locations, determining the nature and/or position of the modifications on the basis of the predefined modification rules and modification keys.
An advantage of the technique of the invention is that a user-specific identifier and thereby the person responsible for the unauthorized copy can be concluded from the information delivered to the user. The advantage obtained by keeping the modifications small is that the information content remains intact and that the unauthorized user will not detect the modifications. When modifications are made in a large number of various locations, the copying and the copier can be exposed even if the information is copied only in part.